Slice the flank steak against the grain into very thin strips.
In a small bowl, combine the chili powder, cumin, garlic powder, sea salt, and black pepper; toss the steak strips in the spice blend until evenly coated.
Thinly slice the red bell pepper and yellow onion into strips.
Heat half of the olive oil in a non-stick skillet over medium-high heat. Add the peppers and onions, sautéing for 3-4 minutes until softened and slightly charred, then remove from the pan.
Add the remaining olive oil to the same skillet. Add the steak strips in a single layer and sear for 2 minutes per side until browned and cooked through. Squeeze the juice of the half lime over the meat and stir.
Wipe the skillet clean and return to medium heat. Place the tortilla in the pan, sprinkle half of the cheese on one side, then top with the steak and vegetable mixture.
Add the remaining cheese over the filling and fold the tortilla in half.
Cook for 2 minutes per side, pressing down slightly with a spatula, until the tortilla is golden brown and crispy and the cheese is fully melted.
Remove from the pan, let rest for one minute, then slice into wedges and serve.